Method of forming single face corrugated board

ABSTRACT

A method of bonding a substantially planar sheet material to a corrugated sheet material using an automated process the method characterised by the steps of
     a) applying adhesive in discrete amounts to the contact points of the corrugated sheet material, and   b) holding the sheet materials together until a bond is formed between them.

FIELD OF THE INVENTION

The present invention relates to a method and machine for forming singleface corrugated board.

BACKGROUND ART

Single faced corrugated paper board is very well known and is usedextensively in industry, especially in packaging where it is used asprotective padding and wrapping. It is also used as a basic component inthe production of many structural objects such as boxes, panels, palletsetc.

Sheets of single faced corrugated paper board can be bonded together toform multilayer corrugated paper boards of various thickness andstrength. One reason for the wide use of such paper board is itsrelatively light weight, rigidity and strength.

Single faced corrugated paper board is made by bonding a fluted sheet,typically of corrugating medium (generally recycled paper) paper, onto aliner sheet. The liner sheet is typically Kraft paper although othermaterials may be used.

In a conventional machine for producing single faced fluted paper board,the fluted sheet is formed by passing a sheet of paper between twocorrugating rollers. The two rollers are arranged such that there is aninter-meshing of the teeth at the periphery of each roller. A sheet ofpaper is fed between the teeth of the rollers which forces the paperinto flutes as the teeth of the rollers intermesh. The fluted sheet isheld in contact with the teeth on the periphery of one of thecorrugating rollers, typically by a vacuum formed within the corrugatingcylinder, at least until the liner is added.

A line of adhesive is applied to the crests of the flutes to bond theliner to the fluted paper. A sheet of liner paper is typically pressedonto the crests by a smooth roller so as to bond the liner with thefluted paper to form a single faced corrugated (or fluted) board.

A limiting factor in this process is the requirement to maintain contactbetween the fluted sheet and the liner for sufficient time for a bond tobe formed. This time can be several seconds or longer at normal roomtemperatures and pressures. However, the time can be reduced by raisingthe temperature during the bonding process and by applying pressure tothe join between the crest and the liner.

High pressure steam is commonly used to heat the cylinders over whichthe fluted paper and liner paper move, raising the temperature of thepaper. Typical operating temperatures for the corrugating rollers can bearound 200° C.

Pressure can be applied to the joint between the liner and each crest bya pressure roller arranged to press the liner against the glued crest.As the contact time between the pressure roller and corrugating roller(which holds the fluted sheet) is relatively short, high pressures aregenerally required to significantly speed up the bonding process.

With this type of arrangement (heating plus high pressure) the bondingtime can be reduced to a few hundredths of a second, allowing high speedproduction of single faced paper board. However, one problem with thisarrangement is that the high pressure exerted by the pressure roller candistort the paper and leave unsightly marks on the surface of the linerpaper, reducing its value.

In some machines other devices, such as endless belts, are used to pressthe liner and fluted sheets together as they move around the corrugatingroller. This extends the period of time pressure is applied, andtherefore lower pressures can be used so as not to deform the surface ofthe paper board.

A typical arrangement of a machine to produce single faced paper boardgenerally as described above is disclosed in U.S. Pat. No. 5,951,817(Thomas).

The machinery depicted in U.S. Pat. No. 5,951,817 has a limited contacttime (and hence bond time) between the fluted sheet and the liner—asevidenced by the fluted sheet/liner combination only being in contactwith a third of the circumference of the corrugated wheel. Such limitedcontact time requires the use of a fast drying adhesive such as a starchbased glue used typically in the industry. Unfortunately, starch basedglues requires the application of heat (say in the order of 150° C. orso) to activate. This leads to disadvantages as discussed below.

Although the use of heat can shorten the time required to form a bondbetween the fluted sheet and the liner, and therefore allow highthrough-put, it does introduce a number of engineering issues whichsignificantly increase the cost of the machinery and the operating costsfor the process. The use of high pressure steam introduces the need forboilers, pipe work, and housing to ensure containment of the steam atall times. There is a need for additional safety measures to ensure thatthe steam is produced and managed correctly and that the heat produceddoes not provide a safety hazard during operation of the machine.Typically a heating engineer is required to operate the boiler andmaintain the heating system, adding the cost of additional skilledlabour, as well as potentially stopping production if such an engineeris not available.

The addition of a high pressure steam system to the basic elements ofthe machine inevitably leads to an increase in the size of the machineand therefore the space required for operation of the machine. Therequirement for more space adds to the operating costs for production ofthe single faced fluted board.

Furthermore high pressure steam is highly corrosive to many materials,and those parts of the machine exposed to the steam, for example thecorrugating rollers, need to be made from appropriate materials. Suchmaterials, for example alloy steel 48 CrMo hardened to HRC 58-62standard, are generally expensive and heavy. A machine made from suchmaterials can require substantial support structure to maintain thestructural integrity of the machine.

A problem with both methods of applying pressure (roller and belt) isthat the applied pressure can spread some of the adhesive away from thecontact line between the liner and the fluted sheet across the crest,thus wetting the surrounding paper. As this spread adhesive is not underpressure (once away from the contact line) and does not necessarily forma bond, further heating can be required in order to dry out the paperand superfluous (spread) adhesive. This adds to the cost of productionand may limit the speed of the process.

The spread adhesive can also get transferred to the surface of thedevice applying the pressure (eg, roller or belt) requiring the surfaceof the device to be continually cleaned. Some adhesive can betransferred to the outer surface of the liner, which can cause problemsduring storage when rolled, as neighbouring sheets can stick togethermaking the product unusable. Further, the adhesive can mark the surface,adversely affecting the appearance and reducing value of the corrugatedboard.

A further disadvantage with conventional machines is that typically thefeed rollers used to feed the paper (both to be fluted and used as aliner) onto the corrugating rollers, and the corrugating rollers, areheated in order to dry out the paper prior to addition of the adhesive.This is to reduce the moisture content of the paper and to produce arapid bonding time. The production of high pressure steam to heat thecorrugating rollers and to pre-heat the paper can require a significantamount of energy.

All of the above factors can add significantly to the cost of singleface fluted board made by conventional processes and machines.

It is an object of the present invention to address the foregoingproblems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited inthis specification are hereby incorporated by reference. No admission ismade that any reference constitutes prior art. The discussion of thereferences states what their authors assert, and the applicant reservesthe right to challenge the accuracy and pertinency of the citeddocuments. It will be clearly understood that, although a number ofprior art publications may be referred to herein, this reference doesnot constitute an admission that any of these documents form part of thecommon general knowledge in the art in New Zealand or in any othercountry.

It is acknowledged that the term ‘comprise’ may, under varyingjurisdictions, be attributed with either an exclusive or an inclusivemeaning. For the purpose of this specification, and unless otherwisenoted, the term ‘comprise’ shall have an inclusive meaning—i.e. that itwill be taken to mean an inclusion of not only the listed components itdirectly references, but also other non-specified components orelements. This rationale will also be used when the term ‘comprised’ or‘comprising’ is used in relation to one or more steps in a method orprocess.

Further aspects and advantages of the present invention will becomeapparent from the ensuing description which is given by way of exampleonly.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided amethod of bonding a substantially planar sheet material to a corrugatedsheet material using an automated process the method characterised bythe steps of:

-   -   a) applying adhesive in discrete amounts to contact points of        the corrugated sheet material, and    -   b) holding the sheet materials together until a bond is formed.

In a preferred embodiment the sheet material is Kraft paper.

Kraft paper is commonly used in the formation of single faced corrugatedboard. However, it is envisaged that other materials may be used withthe present invention and reference throughout this specification tosheet material being Kraft paper only should not be seen as limiting.

For example, the corrugated sheet material may be made from: thin metalsuch as aluminium; recycled paper (in a form commonly referred to as acorrugating medium); and some plastics.

The liner may also be made from a variety of sheet materials includingbut not limited to: clay coated art paper (which may be pre-printed),glassen paper, as well as some plastics.

Reference to a substantially planar sheet material should be understoodto refer to a sheet or web having a substantially flat surface, in whichlies with a single plane a plane (at least when viewed with the nakedeye).

In contrast a corrugated sheet material should be understood to refer toa sheet or web in which the surface is configured into a series ofalternating crests and troughs (i.e. corrugations).

The corrugations in a corrugated sheet used to form a single facedcorrugated paper board are commonly referred to as flutes. Flutes aretypically formed by passing a sheet of Kraft paper through a pair ofcorrugating rolls set in relation to one another so that the teeth ofthe corrugating rolls intermesh-via on either side of the Kraft paper.The shape of the resulting flute is dependent on the shape and size ofthe teeth on the corrugating rolls. For example, (without limitation) aflute can be triangular, sinusoidal, trapezoidal, saw-tooth, rhombic,square or any other suitable repeating undulating shape. Similarly, thesize of the flute is determined by the equi-sized of the teeth and maybe varied depending on the end application for the single facedcorrugated board.

In a preferred embodiment the corrugated sheet material has asubstantially triangular section.

An advantage of forming flutes having a substantially triangular sectionis that it is relatively simple to form using conventionally formedteeth on the corrugating rolls.

Furthermore triangular shaped flutes may have added strength incomparison to some of the other shapes, particular against compressionalong the length of a flute.

The adhesive used to bond a liner to the crests of a fluted sheet, wherethe liner and the fluted sheet are formed from Kraft paper, is typicallya water-based glue.

In the first step of the present invention water-based glue is appliedin discrete amounts to contact points of the corrugated or fluted sheetmaterial. In other words, the adhesive is applied in individuallydistinct amounts which are spaced apart across each crest of the flutedsheet.

The discrete or distinct amounts of glue can vary in form.

In one embodiment, the distinct amounts may be in the form of a smear,or an interrupted line or dash.

By having discrete amounts, less adhesive is applied to the fluted sheetthan is the case with conventional methods. Further, separation betweenthe discrete amounts enables some spread of adhesive to occur on to dryareas once pressure has been applied to the liner and the fluted sheet.

In a preferred embodiment the adhesive is applied across the crest inspaced apart droplets.

It is envisaged that the droplets will be small round, or pear shapedportions of adhesive that adheres to a surface, but this should not beseen as limiting.

The preferred size of the droplet may depend on a number of factors,including the nature of the fluted paper and liner and the type ofadhesive used. However, in all cases the droplet size should be smallenough that the droplet substantially retains its form and does notcollapse under its own weight. This is important as the relatively highvolume to surface area (in comparison say to a strip or line ofadhesive) reduces the rate of evaporation of moisture from the droplet,thus extending the time available for the droplet of adhesive to wet andpenetrate the crest of the fluted paper and the liner prior to theadhesive drying out.

A preferred droplet size is in the order of 0.5 mm³. The preferred gapbetween droplets is calculated by ascertaining the desired adhesivethickness when spread and placing the droplets apart so when the spreaddroplets reach that thickness they just meet each other.

Applying the adhesive as droplets provides at least one or more of thefollowing exemplary advantages:

-   -   Each droplet is applied directly to the crest of the fluted        paper, reducing the amount of adhesive that may inadvertently be        applied to the sides of the crest by other methods and thus also        lessens the amount of wetting of the paper and drying time        required.    -   Using droplets instead of applying a broad strip or line of        adhesive (as in the prior art) may significantly reduce the        amount of adhesive applied to each crest, saving cost.    -   If the same quantity of adhesive as is applied in droplet form        were to be applied as a flat strip across the crest the adhesive        (due to the increased surface area) would dry out in a        relatively short time and may not be able to wet the liner in        order to form a bond. With some adhesives it may be possible for        droplets to remain exposed on the crests of the fluted paper for        several minutes, for example if the machine is stopped for a        short period of time, and still be able to wet the liner and        form a bond when the machine is restarted. This may not be        possible if the adhesive is applied in other forms, such as in a        strip.

Preferably the droplets are spaced apart such that, when the liner ispressed against the crest of the fluted paper, the droplets spread toform a substantially continuous thread of adhesive between the liner andthe crest. The thread formed by compressing the spaced apart dropletsmay result in a substantially finer line of adhesive than that inconventional methods where the strip is applied by a smooth rollerpressing against the crest. This arrangement results in an effective,continuous bond being formed along the crest with a significantlyreduced amount of adhesive used in comparison with conventional methods.

The time taken to form a bond between a crest of the fluted sheet andthe liner will be referred to as the bonding period. The bonding periodfor a particular adhesive depends on the temperature at which the bondis formed and the pressure applied between the crest and liner.

However, the applicant envisages that the present method may be used toproduce single face corrugated board without the application ofheat—i.e., substantially at ambient temperature—say 5° C.-30° C. Atambient temperature the bonding period may vary as a function of theamount of glue applied (as droplets) and the pressure applied betweenthe liner and the crest of the flute, with shorter bonding periods forhigher applied pressures and less glue.

It should be appreciated that the choice of adhesive of the presentinvention is important. As noted in the Background Art, starch basedadhesives require a activation temperature in the order of 150° C. Thus,such an adhesive would not be desirable for use with the presentinvention. Suitable adhesives that can set rapidly at room temperature,and has the required strength are discussed later on in thisspecification.

It is of significant advantage of the present invention that it enablesthe board to produce without the application of heat. As discussedfurther in the specification, this removes the need for expensivemachinery and energy requirements. It should be appreciated that it isthe recognition that the application of discrete amounts of adhesiveenables the significant advantage to be achieved through shorter bondingtime at ambient temperatures.

In the second step of the method according to the present invention theliner is pressed against the fluted sheet for a time sufficient to allowa bond to form. This may be achieved by a variety of means.

In a preferred embodiment the planar sheet is pressed against thecorrugated sheet by a tensioned endless belt.

The exertion of pressure on a liner to press it against a fluted sheetby use of a tensioned endless belt, is well known in the art and theequipment to do so need not be discussed in further detail.

The pressure may be adjusted to be at, or just below, the maximumpressure that can be applied without deforming the paper (liner andfluted papers). Excessive pressure can lead to creasing and/or tearingof the paper. The maximum pressure will vary depending on the materialused for the liner and fluted paper.

In a preferred embodiment the sheet materials are held together for aperiod not less than two seconds.

The applicant has found that using an endless belt tensioned to hold theliner firmly against the crests without damaging the liner, and withsuitable commercially available adhesive, the liner and fluted sheetneed to be pressed together for a period (pressing time) longer thanabout two seconds at room temperature to ensure the liner and flutedboard form a good bond.

Typically, for pressing times less than around two seconds, or if thepressure between the sheets is too little, a single faced corrugatedboard will not be formed. In such cases, the tension in the corrugatedsheet is sufficient to break the bond, so that the liner comes away fromthe fluted sheet.

For practical purposes at room temperature holding times between twoseconds and four seconds are desirable, with a pressing time of aroundthree seconds being preferred. Pressing times greater than four secondsmay be used, but are not preferred as such times may significantlyreduce the production rate of single face corrugated board.

A pressing time of around three seconds is significantly slower thanthat achieved by some prior art machines through the use of acombination of high temperature and high pressure. However, an advantageof the present invention is that it may produce quantities of singleface corrugated board at an acceptable rate at room temperature. Thisprovides the advantage of a process and apparatus which may producesingle face corrugated board at a reduced cost and in a safe andenvironmental friendly manner.

The inventor considers the combination of the discrete application ofadhesive droplets with an increased holding time (as compared toconventional machines) enable an adhesive to be used that can set atroom temperature.

In a preferred embodiment the adhesive is a water-based dispersioncontaining vinyl acetate copolymer.

A water-based adhesive containing vinyl acetate copolymer in dispersionmay be preferred as, under normal use, it is a non-hazardous substance,and therefore can be used safely provided normal ventilation isprovided.

Vinyl acetate copolymer dispersions can be relatively quick setting atroom temperature and do not require a high activation temperature—unlikestarch based glues. They have a low viscosity, good adhesion and a longopen time. A relatively low viscosity is required to allow the adhesiveto flow readily, (e.g., when being transferred from an applicator to thefluted sheet) while a good adhesion provides the ability to adherequickly to a surface.

The open time is a measure of the time, under normal temperature andpressure, that the adhesive can have an exposed surface before it losesits ability to wet the opposing surface and penetrate into the opposingsurface fibres. This wetting and penetration is required to form aneffective bond between the fluted paper and the liner. An adhesivehaving a relatively long open time is preferred as the adhesive may beopen to the atmosphere for some time prior to application to the flutes.

Preferably the adhesive is Adhesin™ Z9129W, a vinyl acetate copolymersupplied by Henkel New Zealand Limited. The applicant has found thatAdhesin™ Z9129W has the required viscosity, and long open time requiredfor use with the present invention. For example, Adhesin™ Z9129W has aviscosity in the range 2100-2200 m·Pa·S and an open time of between 0.5to 1 minute. However, it is envisaged that other adhesives havingsimilar properties may also be used.

Applying an adhesive (such as Adhesin™ Z9129W) in droplet form to thecrest of a fluted sheet, and pressing a liner against the crest foraround 3 s to form a bond between the fluted sheet and liner, provides anumber of significant advantages over the prior art. In particular, themethod may be used to produce single face corrugated paper board at roomtemperature. As a result there is no need for heating of the corrugatingrolls or drying out of the single face corrugated board. This maytranslate into a significant reduction in energy use and hence lower theproduction cost of the paper board.

According to another aspect of the present invention there is anapplicator for applying adhesive in a discrete amount, including

a rollercharacterised in thatthe outer surface of the roller has a contoured surface.

The contoured surface can come in a number of forms and in oneembodiment they may be dimpled or an irregular surface. In someembodiments the surface may be in the form of a U-shaped groove.

Preferably however, the contoured surface is in the form of finecorrugations reminiscent of a square wave.

Reference to a corrugated surface should be understood to refer to asurface formed into a series of crests and troughs.

In a preferred embodiment the crests (and troughs) are substantiallyparallel and extend around the circumference of the roller.

In a preferred embodiment the crests form a spiral.

A series of crests may be formed across the surface of the roller bymaking a spiral cut around the surface of the roller in a similar mannerto forming a (non-tapered) screw thread. A spiral cut, or screw thread,may be relatively easy to machine into a smooth surface of a roller.This may reduce the cost of forming an applicator in comparison withother types or arrangements of crests.

In other embodiments the crests may form concentric circles.

Preferably the crests and troughs may be formed by cutting (or otherwiseshaping) a ‘V’ or square shaped groove in the surface of the applicator.The actual shape of the groove is not critical, but a ‘V’ shaped grooveis preferred as it is relatively easily cut into a smooth cylindricalsurface.

In use, adhesive may be supplied to the applicator by a smooth surfacepick-up roller.

For example, spray nozzles may be used or an air blade that passesthrough a trough.

In an embodiment that has a pick up roller, the pick-up roller ismounted adjacent to an adhesive bath such that as the pick-up rollerrotates its outer surface is coated with adhesive.

The applicator is mounted with respect to the pick-up roller such thatthe crests of the applicator make firm contact with the surface of thepick-up roller. In this way adhesive is transferred from the surface ofthe pick-up roller into the grooves in the surface of the applicator,with little or no adhesive being applied to the crests of theapplicator.

The gap between the pick up roller and the roller that forms part of theapplicator determines the amount of glue being applied.

The mounting of the applicator is also such that the crests of theapplicator make firm contact with the crests of the fluted sheet on thecorrugating roll. With this arrangement as the applicator rotates itpicks up adhesive in the grooves on its surface as it contacts thepick-up roller, and then deposits the adhesive as droplets onto thecrests of the fluted sheet.

The amount of adhesive for each droplet may be determined by the size(width and depth) of each groove, while the separation of the dropletsmay be determined by the separation of adjacent grooves.

It should be appreciated that the groove should be sufficiently shallowto avoid to much glue being deposited onto the paper. In a preferredembodiment, the depth of the groove is only 0.5 mm and width of thegroove is only in the order of 1 mm. This may of course vary inaccording to the requirements of the invention.

In a preferred embodiment the crest may take the form of a sharp edge.

Preferably, the ‘V’-shaped grooves are arranged such that each grooveabuts the adjacent grooves to form a sharp edge so that a sectionthrough a series of grooves forms a continuous zigzag pattern. Thisarrangement may provide the minimum separation between adjacent droplets(for a given width of each groove).

In some other embodiments the crests may have a flat section, in whichcase the separation of the droplets may be correspondingly larger.

According to another aspect of the present invention there is provided amachine for making single faced corrugated board by bonding a corrugatedsheet material having one or more crests onto a substantially planarsheet, the machine including

an applicator configured to apply adhesive to each crest of thecorrugated sheet material, anda pressing mechanism for pressing the planar sheet against the crest ofthe corrugated materialcharaterised in thatthe applicator is configured to apply adhesive in discrete amounts tothe crest of the corrugated sheet material and the pressing mechanism isconfigured to press the liner sheet against the crest until a bond isformed between them.

A machine for making single face corrugated board according to thepresent invention has many features in common with some prior artmachines. In particular a fluted sheet is formed by passing a sheetmaterial between the intermeshed teeth of first and second corrugatingrolls. The fluted sheet is held against the second corrugating roll,which typically has a larger diameter than the first corrugating roll,by a vacuum created inside the second corrugating roll.

As the second corrugating roll rotates the fluted paper passes anapplicator where adhesive is applied to the crests of the fluted sheet.

In a preferred embodiment the applicator includes a roller having acorrugated surface substantially as described above.

The corrugated surface of the applicator (as described above) isconfigured to apply droplets of adhesive across a crest of a flutedsheet. This is in contrast to conventional machines in which theapplicator typically has a knurled surface so as to spread a relativelybroad strip or line of adhesive across the crest of the flute.

The applicator is rotatably mounted such that the outer surface (crests)of the applicator press against the crests of the fluted paper held onthe second corrugating roll.

In a preferred embodiment the pressing mechanism is a tensioned endlessbelt.

An endless belt may be configured to move around a plurality of rollers,the rollers arranged such that the belt is held in contact with theliner as the liner and fluted sheet move around the periphery of thesecond corrugating roll.

This arrangement may be achieved by placing two end guide rollers spacedapart around the periphery of the second corrugating roller, the spacingdefining the distance over which the belt contacts the liner. The twoend guides may be mounted so as to provide pressure (via the belt) ontothe liner as it initially contacts the fluted sheet, and again justbefore the single face fluted sheet is removed from the secondcorrugating roll.

The belt may be tensioned by adjustment of one or more of the remainingrollers so that the belt applies pressure to the liner to press itagainst the fluted sheet.

As there is no heating required, a standard rubber belt may be used,rather than the more exotic materials used with heated rollers. Use of astandard rubber belt may result in less damage to the surface of theliner, and hence a superior product.

In other embodiments the endless belt may be made of plastics orsynthetic material.

An advantage of the present method, when applied at room temperature, isthat the endless belt may be formed using heat sensitive materials suchas plastics, synthetics and some rubbers that would not be suitable inconventional, heated processes.

In a preferred embodiment the endless belt is configured to press thesheet materials together for more than 2 seconds.

In a preferred embodiment the endless belt is configured to press thesheet materials together for a time between about 2 seconds and about 4seconds.

Generally with the belt tensioned tightly against the liner, the timetaken to form a bond at normal room temperature is more than 2 seconds.In general, a time of around 3 seconds is preferred as this has beenfound to provide a reliable bond throughout the normal range of ambienttemperatures—say 5° C.-30° C.

The production rate of single face corrugated board using such a machinedepends on several factors, including the diameter of the secondcorrugating roll, the percentage of the periphery of the secondcorrugating roll that the belt is pressed against, and the speed ofrotation of the second corrugating roll. These factors may be varied sothat pressure is applied between the liner and the fluted sheet for thetime required to form a bond at room temperature. Once a convenientarrangement has been found, the production rate can be determined byscaling the factors. For example, if the percentage coverage of thesecond corrugating roll by the endless belt is fixed, the productionrate can be varied by choosing an appropriate diameter and speed ofrotation of the second corrugating roll.

The main advantage of the method of the present invention is that itprovides the ability to form single face corrugated board at roomtemperature at a rate that may be comparable to conventional methods.

In other words, the present invention allows the efficient production ofsingle phase corrugated board without requiring additional heat to beapplied to the process.

This feature is achieved by the combination of applying adhesive to thefluted paper in droplet form, followed by pressing the liner against thefluted sheet until a bond is formed. Application of droplets alone(without applying pressure), or applying adhesive as a strip or line (asin conventional methods) followed by pressing, both may result in thetime taken to form a bond (and hence form single face corrugated board)is too long to be practicable commercially.

However by combining the two aspects, the time required to form a bondmay be reduced to around 3 seconds at room temperature.

The ability to form single face corrugated board at room temperaturesprovides one or more of the following advantages over the prior art.

-   -   Saving in energy cost and a lower carbon footprint than        conventional methods through removing the need to heat the        corrugating rolls and to dry the paper. This removes the        requirement for high pressure steam which is very energy        intensive.    -   Saving in the cost of machinery. As heating is not required,        there is a significant saving in not requiring boilers, pipe        work and containment for high pressure steam. Further, as the        machine is operated at room temperatures it can be constructed        from simpler and less expensive materials, such as (without        limitation) ceramics, plastics or wood. As such materials are        generally easier to form and lighter than the materials        (generally hardened steel) used in conventional machines that        use steam, the machine may be cheaper to make and be supported        by a lighter frame, again saving on material cost.    -   Saving in space. Removal of the apparatus associated with        heating may result in a machine that requires less space than        conventional, heated machines.    -   Improved safety. As the machine operates at room temperature,        the hazards associated with production and use of high pressure        steam are no longer present.    -   Saving in operating costs. Apart from a reduction in energy        usage, the present method may result in significantly less        consumption of adhesive.

Importantly a machine according to the present invention may be of asize and cost that makes it suitable for on-site production of singleface corrugated board. Conventional heated machines are typically large,energy intensive and expensive to construct and operate. As aconsequence such machines are commonly operated in centralisedlocations, with the single faced corrugated board, or products made fromit, transported to consumers.

The size of the machine according to the present invention is scalable,mainly because no heating apparatus is required. Hence, a machineaccording to the present invention may be of a size suitable forinstallation and operation on the site of the consumer, for example tomake packaging on site. This may provide savings to the consumer, assupply would be controlled by the consumer, and there would be notransport and handling costs from off-site production.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from thefollowing description which is given by way of example only and withreference to the accompanying drawings in which:

FIG. 1 shows a schematic side elevation of part of a single facermachine according to one embodiment of the present invention; and

FIG. 1A shows a close up of the applicator portion of the machine inFIG. 1 according to one embodiment of the present invention.

FIG. 2 shows a schematic view of an edge portion of an applicatoraccording to one embodiment of the present invention.

FIG. 3A shows a schematic side elevation of a fluted sheet with dropletsof adhesive applied to the crests;

FIG. 3B shows a schematic perspective view of a fluted sheet with a lineof spaced apart droplets of adhesive along two of the crests; and

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A portion of a machine for forming single faced corrugated board isgenerally shown by arrow (1) in the schematic side elevation shown inFIG. 1.

A first corrugating roller (2) has teeth (2′) arranged around theperiphery of the first corrugating roller (2), the teeth (2′) extendinglaterally across the width of the first corrugating roller (2).

A second corrugating roller (3) has teeth (3′) around its periphery. Thediameter of the second corrugating roller (3) is substantially largerthan the diameter of the first corrugating roller (2).

The corrugating rollers (2 and 3) are arranged such that teeth (2′) ofthe first corrugating roller (2) intermesh with the teeth (3′) of thesecond corrugating roller (3) in the region indicated by number (16).

The first corrugating roller (2) is powered to rotate in a clockwisedirection and the second corrugating roller (3) is powered to rotate inan anticlockwise direction, as indicated by the respective dashedarrows.

A planar sheet material, in the form of a sheet of Kraft paper (7), isfed around the first corrugating roller (2) and between the intermeshedteeth in the region of arrow (16). The action of the teeth as theyintermesh folds the Kraft paper into a series of crests to form a flutedsheet (8).

The Kraft paper may be recycled or virgin paper and ideally in the orderof 90 to 150 gsm.

The second corrugating roller (3) includes open passageways (not shown)so that a partial vacuum can be created inside the corrugating roller(3) by connecting a vacuum pump (not shown) to one end of thecorrugating roller (3). This partial vacuum inside the secondcorrugating roller (3) is used to hold the fluted sheet (8) in placeagainst the teeth (3′) of the second corrugating roller (3).

An applicator in the form of a glue roller (4) has an outer surfaceconfigured as a series of crests and troughs which extend around thecircumference of the roller. The crests are formed by a spiral ‘V’shaped cut extending around and across the surface of the glue roller(4).

Adjacent ‘V’ shaped troughs (21, 22) meet at a line to form the crests(20) of the roller (4). Each crest (20) has a sharp edge as shown inFIG. 2, such that the series of crests form a zigzag pattern in crosssection.

The glue roller (4) is rotatably mounted alongside the secondcorrugating roller (3), the axis of rotation of the glue roller (4)being substantially parallel to the axis of rotation of the corrugatingroller (3). The axis of the glue roller (4) is displaced from the axisof the second corrugating roller (3) by a distance such that the crests(20) of the glue roller (4) hold against the crests of the fluted sheet(8) held in the teeth of the second corrugating roller (3).

A pick-up roller (5) is rotatably mounted on an axis substantiallyparallel to the axis of the glue roller (4), and is arranged such thatthe surface of the pick-up roller (5) makes firm contact with each crestof the glue roller (4).

A bath (6) contains adhesive in the form of Adhesin™ Z9129W. The bath(6) is arranged such that the outer surface of the pick-up roller (5) iscoated with Adhesin™ Z9129W as the pick-up roller (5) rotates.

The first corrugating rollers (2), second corrugating roller (3), theglue roller (4) and pick-up roller (5) all have a width comparable tothe width of the fluted sheet (8).

Adhesive is transferred from the surface of the pick-up roller (5) intothe troughs (21, 22) of the glue roller (4). The adhesive is carried bythe glue roller (4) as it rotates at a peripheral speed corresponding tothe corrugating roller when the glue roller contacts a crest of thefluted paper (8) along the contact line (9), at which point the adhesiveis transferred from the troughs (21, 22) onto the crest (18) in the formof droplets.

A schematic side elevation of a sheet of fluted paper, in which droplets(19) have been deposited onto the crests (18), is generally indicated byarrow 17 in FIG. 3A.

FIG. 3B shows a schematic perspective view of a plurality of discretedroplets (19) deposited along a crest (18) of a sheet of fluted paper.

Referring back to FIG. 1, a second planar sheet of Kraft paper, in theform of a liner (10) is pressed against the fluted sheet (8) by atensioned belt assembly generally indicated by arrow (17).

The endless belt (13) is held in place against the periphery of thesecond corrugating roller (3) by the action of the first guide endroller (11), second guide end roller (12), two guide rollers (14) and atensioning roller (23) as known in the prior art.

The separation of the first guide end roller (11) from the second guideend roller (12) determines the length over which the endless belt (13)applies pressure to the liner (10). This separation correspondsapproximately to three quarters of the periphery of the secondcorrugating roller (3), this being approximately the maximum lengthavailable (so as to leave room for the first corrugating roller (2) andthe glue roller (4).

Tension is applied to the endless belt (13) by adjusting radially (withrespect to the axis of the second corrugating roller (3)) the positionof the tensioning roller (23).

In practice tension in the belt (13) is adjusted to the point wheredamage, typically in the form of creasing or tearing of the liner and/orfluted paper, occurs. The tension, is then reduced by backing off thetensioning roller (23) to the lowest tension below this threshold wheredamage does not occur. The amount of tension applied to belt (13) toachieve the correct pressure of the belt (13) against the roller (3)depends on many factors including the nature of the sheet materials usedfor the liner and fluted sheets. The joining of the liner (10) to flutedpaper (8) forms corrugated board (15).

A pick (24) is located in the vicinity immediately after the guide endroller (12). The pick (24) is used to help release the bonded singleface corrugated board (15) from being held by the vacuum inside thesecond corrugating roller (3).

The rate of production of single face corrugated board (15) in thisarrangement is determined by the diameter and rotation speed of thesecond corrugating roller (3). With the endless belt (13) extendingaround approximately three quarters of the periphery of the secondcorrugating roller (3), this fixes the rotation time at around 20revolutions per minute, independent of the diameter of the roller (3).However, the amount produced is dependent on the diameter, D (measuredin metres), of the roller (3) and is given (for the configurationdescribed above) by 20πD metres per minute, ie., around 63 times thediameter of roller (3) (measured in metres) metres per minute.

For example, a second corrugating roller (3) having a diameter of 1.6 mmay produce around 100 m/min of singled face paper board.

FIG. 1A is a close-up of the machine shown in FIG. 1 and shows moreclearly the corrugations on the glue roller 4A.

Aspects of the present invention have been described by way of exampleonly and it should be appreciated that modifications and additions maybe made thereto without departing from the scope thereof as defined inthe appended claims.

What is claimed is:
 1. A corrugated sheet product comprising: at leastone planar sheet; a corrugated sheet; wherein the planar sheet is bondedto the corrugated sheet via a water based vinyl acetate copolymerdispersion adhesive which is applied to the crests of the corrugatedsheet in discrete droplets having dimensions of 0.5 mm³.
 2. A corrugatedsheet product as claimed in claim 1 wherein the corrugated sheet productis single face paper board.